This invention relates generally to fiber optic gyroscope rotation sensing systems. More particularly, this invention relates to the processing of signals output from a fiber optic gyroscope to measure rotation rates. Still more particularly, this invention relates to an improved dither system and method using a low amplitude dither signal in a fiber optic gyroscope signal processing system.
U.S. Pat. No. 5,020,912, which issued Jun. 4, 1991 to George A. Pavlath, one of the inventors of the present invention, discloses a deadband circumvention technique for a closed loop fiber gyro that uses deterministic phase modulation. A periodic zero mean dither signal is input to an integrator that also has the gyro demodulated rate signal as an input. A key requirement is that the gyro loop bandwidth be greater than the dither frequency, which in turn is larger than the sampling frequency. Ideally the dither frequency is at least ten times the sampling frequency, and the loop bandwidth is at least ten times the dither frequency. If these conditions are not met, problems occur in operation of the fiber optic gyro as a rotation sensor. The problems include saturation of the front end of the gyro control loop for large dither amplitudes due to the limited loop bandwidth and finite analog to digital converter input range and large dither residuals in the output if there are not precisely an integer number of dither cycles in the sampling period. Saturation in the control loop leads to increased random walk through failure to cancel the dither signal and other undesirable nonlinearities. Decreasing the amplitude of the dither signal to avoid saturation could result in there not being sufficient dither to break up the deadband at high sampling rates. Applying a small amplitude dither signal for a time longer than the sampling time causes each sample to include a large amount of residual dither. The disclosure of U.S. Pat. No. 5,020,912 is incorporated by reference into the present disclosure.